Hydraulic actuation system

ABSTRACT

A hydraulic actuation system, especially for actuating the clutch of a vehicle, containing a master cylinder unit, a slave cylinder unit, a hydraulic medium line connecting the two cylinder units and a throttle valve which is used to alter the flow resistance between the cylinders of the master cylinder unit and the slave cylinder unit.

The present invention relates to a hydraulic clutch system, inparticular for actuating a vehicle clutch. Furthermore, the presentinvention relates to a device for connecting a pipe-shaped hydraulicmedium line to a connector on a housing, in particular in a hydraulicsystem according to the present invention.

Hydraulic actuation systems having a master cylinder unit, which is, forexample, operated by a pedal using the foot, and which is connected viaa pressure medium line to a slave cylinder unit, which actuates anassembly such as a vehicle clutch, transmission, or brake, have manyapplications. Actuation systems of this kind, in particular actuationsystems for actuating a vehicle clutch, are designed to ensure that theassembly in question can be actuated safely and comfortably.

One problem encountered when vehicle clutches are actuated hydraulicallyis that the engine stalls if a clutch pedal is actuated too quickly toengage the clutch.

The object of the present invention is to create a hydraulic actuationsystem, in particular for actuating a vehicle clutch, which allowsactuation to be carried out in a carefully measured manner.

This object is achieved with a hydraulic actuation system, in particularfor actuating a vehicle clutch that includes a master cylinder unit, aslave cylinder unit, a pressure medium line connecting the two cylinderunits, and a throttle valve for adjusting the flow resistance betweenthe cylinders of the master cylinder unit and the slave cylinder unit.With the actuation system according to the present invention, thethrough-flow resistance between the cylinder units and thus the behaviorof the hydraulic transfer section is adjustable based on therequirements in question by designing or controlling the throttle valveappropriately.

It is advantageous that the throttle valve is actuated by an actuatorcontrolled by a control unit that is connected to a sensor which detectsthe engine speed and if necessary adjusts the through-flow cross sectionbetween the master cylinder unit and the slave cylinder unit during thestarting-off procedure as a function of the engine speed curve. In thisway, the through-flow cross section between the master cylinder unit andthe slave cylinder unit may be adjusted as a function of the movement ofthe piston in question. The signals for controlling the device may ofcourse also be generated using sensors already present in the vehicle,e.g., engine sensors, transmission input sensors, transmission outputsensors and/or wheel speed sensors.

If the actuation system according to the present invention is used toactuate a vehicle starting clutch, it is advantageous that the sensordetects the engine speed and, if the engine speed curve exceedspredefined limiting values as the clutch engages, the control unittriggers the actuator in the direction of a reduction of thethrough-flow cross section. This means that the engine's requiredincrease in torque as the clutch engages does not have to increaseabruptly, and hence stalling of the engine is avoided.

It is advantageous that, if the engine speed curve exceeds predefinedlimiting values as the clutch engages, the control unit of theaforementioned actuation system triggers an actuator for adjusting theoutput of an internal combustion engine of the vehicle in the directionof an output increase. This further reduces the risk of stalling theengine, i.e., the internal combustion engine.

It is advantageous that the control unit is connected to further sensorsfor detecting the rotational speed of a vehicle wheel and/or atransmission ratio so that the through-flow cross section of thehydraulic section of the actuation system is adjustable optimally basedon the prevailing operating conditions and in accordance with therequirements in question.

In a modified embodiment of an actuation system according to the presentinvention, a valve element of the throttle valve is movably mounted in abore hole that extends roughly at right angles to a connector bore holeleading into the working chamber of one of the cylinder units and isdesigned and works in conjunction with walls of the bore hole in such away that it is moved in one or another direction into contact with astop edge by a hydraulic medium flow between the two cylinder units, andas a result a flow cross section made available by the valve element isreduced when it rests against the stop edge. With the aforementionedembodiment of the throttle valve, the axial space occupied by thecorresponding cylinder unit is only minimally increased by the throttlevalve, and furthermore the design is straightforward and very reliable.

It is advantageous that the valve as a whole is pipe-shaped, has anaxial through-channel and is movably mounted so that hydraulic mediumflowing out of the corresponding working chamber flows through thethrough-channel, and hydraulic medium flowing into the correspondingworking chamber moves the valve element so that its end face restsagainst a wall that encloses the bore hole, so that the through-channelis at least partially closed and the hydraulic medium flows through aradial opening in the wall of the through-channel.

In a further refinement of the aforementioned throttle valve, the borehole which bears the valve element is positioned in the housing of thecorresponding cylinder unit and the pressure medium line is connected tothe bore hole.

It is advantageous that the throttle valve is assigned to the mastercylinder of a vehicle hydraulic clutch actuation system and reduces theflow cross section of a flow of hydraulic medium into the mastercylinder.

A particularly straightforward design of a device for connecting apipe-shaped hydraulic medium line to a connector on a housing, which inparticular may be used in a hydraulic system of the type describedabove, includes an insertion channel in a cylindrical attachment part ofthe housing for insertion of a pipe, an annular space being formedbetween the outside of the pipe and the inside of the insertion channel,this being delimited axially inward by a radial annular surface, alocking element which is cylindrical as a whole and which is insertableinto the insertion channel and which in its inserted state protrudeswith its front end-section into the annular space and with its rearend-section lies outside the cylindrical attachment part, at least onesealing ring which may be positioned in the annular space between an endface of the locking element and the radial annular surface, and alocking sleeve which is rotatable relative to the locking element and isrotatable from an unlock position, in which the pipe is insertablethrough the locking sleeve and locking element beyond the annularsurface of the attachment part and into the insertion channel, to a lockposition in which the pipe is held axially against the attachment partby the locking element and/or locking sleeve.

The aforementioned device has a straightforward and cost-effectivedesign and has the additional advantage that even when the pipe has notbeen installed, the sealing ring is held against the pre-assembledassembly that includes the housing and the locking element and, ifapplicable, the locking sleeve, and is thus protected against dirt anddamage.

It is advantageous that the front end-section of the locking element inits inserted state extends back through the annular space of thecylindrical attachment part so that the locking element cannot be movedoutward because it rests against the cylindrical attachment part in aform-locking manner.

It is advantageous that the annular space has in the outward direction aradial holding surface against which a counter-surface on theend-section of the locking element rests. This ensures that the lockingelement may be positioned against the attachment part without anyproblem.

If the rear end side of the locking element has radially inward a radialstop surface against which a projection on the pipe rests, the pipe maybe positioned easily and reliably.

It is advantageous that the radial stop surface of the locking elementdelimits an annular space which overlaps the projection on the pipe.This ensures that the pipe cannot be shifted outward.

The projection is formed in a particularly straightforward manner by anannular bulge.

It is advantageous that the locking element has at least two fingerslocated diametrically opposite one another which rest against theoutside of the cylindrical attachment part and work in conjunction withfingers on the locking sleeve so that in the locking sleeve's lockposition they are pressed into engagement with the outside of thecylindrical attachment part in a form-locking manner.

The present invention, which may generally be used for all kinds ofhydraulic actuation systems, in particular those for actuating a vehicleclutch, is described in greater detail below by way of examples and withthe help of schematic drawings.

FIG. 1 shows a schematic drawing of a hydraulic actuation system of avehicle clutch;

FIGS. 2 and 3 show side views of a throttle valve with the valve elementin two different positions;

FIGS. 4 and 5 show side views of a further embodiment of a throttlevalve with the valve element in two different positions;

FIG. 6 shows an axial section through a connector device;

FIG. 7 shows a perspective view of the device shown in FIG. 6; and

FIG. 8 shows a longitudinal section through a pipe having a projectionformed by a bulge.

As shown in FIG. 1, a hydraulic actuation system for a clutch includes amaster cylinder unit 10, which is connected to a slave cylinder unit 12via a hydraulic medium line 14. A clutch 16 is actuated hydraulicallywhen master cylinder unit 10 is acted upon by an actuating element 18,which may be a foot pedal, an actuator, for example an electricalactuator or similar. When actuating element 18 is actuated, a movablepiston 24 in cylinder 22 of master cylinder unit 10 is moved by a pistonrod 20 to the left as shown in FIG. 1 so that pressure builds up incylinder 22 and is conveyed via hydraulic medium line 14 through athrottle valve 26 into slave cylinder unit 12. It is advantageous thatslave cylinder 12 is, as shown, positioned concentrically around atransmission input shaft 28 and rests axially on a transmission housing(not shown) so that the necessary release force may be exerted via arelease bearing of clutch 16, i.e., on its release elements, e.g., disksprings, in a manner known heretofore.

When clutch 16, which is positioned concentrically with a crankshaft 30of an internal combustion engine 32, is engaged, transmission inputshaft 28 transfers the torque of internal combustion engine 32 to atransmission (not shown) and from that to the drive wheels of a vehicle.

A pressure medium reservoir 34 supplies pressure medium in a manner thatis known heretofore, and is connected to master cylinder 10 when thelatter is in the inoperative position, i.e., no pressure is beingexerted on slave cylinder 12. In this position, pressure medium is ableto flow back into master cylinder unit 10. When master cylinder unit 10is actuated, pressure medium reservoir 34 is separated from mastercylinder unit 10 by a valve (e.g., a covered snifter hole) which is notshown.

Throttle valve 26 includes a valve element 40 which is pushed into theopen position by a spring 42 and which has a shaft that functions as anarmature for an electromagnet 44. Electromagnet 44 is triggered by acontrol unit 46, the inputs of which are connected to a sensor 48 fordetecting the engine speed of piston rod 20 and actuating element 18, asensor 48 for detecting the rotational speed of a vehicle wheel (notshown), and a sensor 52 for detecting the gear, i.e., gear ratio, of atransmission (not shown). A further output of control unit 46 isconnected to an actuator 54 for actuating a power control element ofinternal combustion engine 32, e.g., a throttle.

Electronically actuated throttle valve 26 functions as follows:

During the clutch's engaging procedure, the engine speed is detected. Ifthe engine speed falls below an rpm limiting value which is dependent onthe drop rate of the engine speed, current is applied to electromagnet44 so that valve element 40 moves into a flow cross section formed by ahousing of throttle valve 26 and reduces it.

The flow of hydraulic medium through line 14 is thus reduced so thatclutch 16 engages more slowly, thus reducing the danger of stallinginternal combustion engine 32.

Actuator 54 is optional. If it is present, it is advantageous thatsimultaneously with the increasing closure of throttle valve 26 thepower control element is opened so that the engine speed is increased.This provides additional help in preventing stalling. The speed ofopening of the power control element is, for example, proportional tothe speed of closure, i.e., speed of engagement of the clutch.

Sensors 50 and 52 are also optional. If the wheel rotational speed andthe gear position are detected, the throttle valve may be actuated in amanner appropriate to the operating situation, for example, thethrough-flow cross section of line 14 may be limited over a longerperiod if the vehicle is starting off in first gear than is the casewhen shifting between other gears, it also being possible for the degreeof throttling, i.e., reduction of cross section, to also be dependent onthe vehicle speed.

Various control strategies are feasible for the throttle valve, forexample path control as a proportional valve, or pulses of theelectromagnet having different frequencies, or 2-point control withopen/closed only. Furthermore, various strategies are feasible for pathmeasurement for master cylinder unit 10, for example, continuous pathmeasurement, which may at the same time replace a currently customarybrake light switch, and moreover the signals may be used in conjunctionwith an engine control system for improving driving comfort. In astraightforward form, 2- or 3-point measurement is sufficient, as foundcurrently with pedal switches or at the master cylinder unit.

Active throttle valve 26 as described, which may be designed andactuated in a variety of ways (globe valve, turning valve etc.), isadvantageous when starting off, i.e., for preventing stalling of theengine, and furthermore may also advantageously be used when shiftingbetween higher gears.

A further advantageous application of the active throttle valve is thatit may be used to suppress back-engagement between the engine and theclutch pedal, e.g., as caused by engine vibration. Excessively highpressure in hydraulic medium line 14, which in FIG. 1 is shown to theleft of throttle valve 26, as may be induced by vibration, may bedetected by a pressure sensor.(not shown) and converted into athrottling of the through-flow cross section.

FIGS. 2 and 3 show cross sections through a passive throttle valve 60,the valve element of which is in two different positions. An axial crosssection through a part of master cylinder 22 is shown. From workingchamber 62 of a master cylinder 22, connector bore hole. 64 leads into afurther bore hole 66 which is roughly at right angles to connector borehole 64 in the housing of cylinder 22 and which, as shown in FIG. 2, isclosed off from above by a stopper 68 so that a fluid-tight seal isensured. Stopper 68, which may be, for example, screwed into bore hole66, has an end face 70 which is roughly flush with the upper side ofconnector bore hole 64. A pipe- or sleeve-shaped valve element 72 ismovable in bore hole 66 via a collar 74.

FIG. 2 shows the fully opened position of throttle valve 60 assumed byvalve element 72 when hydraulic medium flows from working chamber 62into bore hole 66, to which as shown in FIG. 2 hydraulic medium line 14(FIG. 1) is connected at the lower end. In the fully open position,collar 74 rests against a step 76 of bore hole 66 so that the openingmovement of valve element 72 is limited. Of course valve element 72 isribbed on its outside beneath collar 74 and/or bore hole 66 is ribbedbelow step 76 so that hydraulic medium between the collar and the stepis able to escape. As can be seen, when valve element 72 is in the openposition the entire cross section of a through-channel 78 through valveelement 72 is available.

When the flow direction of medium is reversed, i.e., it flows out ofbore hole 66 into working chamber 62, valve element 72 moves out of theposition shown in FIG. 2 into the position shown in FIG. 3 in which itsupper annular end face 80 rests against end face 70 of stopper 68. Inthis case there is only a small flow cross section available for themedium to flow through through-channel 78, this being formed by one or aplurality of recesses 82 on the upper edge of valve element 72. Ofcourse recess or recesses 82 do not have to be located directly on theupper edge of valve element 72, but rather may be in the form of one ora plurality of radial bore holes above collar 74.

The functioning of throttle valve 60 as shown in FIGS. 2 and 3 is as awhole similar to that of throttle valve 26 shown in FIG. 1, with thedifference that throttle valve 60 functions passively. When medium flowsrapidly into working chamber 62, for example when the clutch is engaged,valve element 72 moves into its upper resting position and reduces thethrough-flow cross section to a minimum defined by recess 82. In thisway, the dynamic torque that the engine has to provide, in particularwhen the vehicle starts off with the clutch pedal having been releasedvery rapidly, is limited.

Of course various embodiments of valve element 72, which is moved by thepressure medium flow, i.e., by the pressure of the pressure medium, andof throttle valve 60 are feasible. For example, valve element 72 mayhave a plurality of axial through-flow channels which in the positionshown in FIG. 2 are all open and at least a few of which are closed inthe position shown in FIG. 3. In addition, a spring may be provided topre-tension the valve element in one of its end positions.

The design of throttle valve 60 which is integrated into the housing ofcylinder 22 is extremely compact and straightforward and only minimallylengthens cylinder 22 in its axial direction by the diameter of borehole 66.

FIGS. 4 and 5, which largely correspond to FIGS. 2 and 3, show amodified embodiment of a valve element. Collar 74 of valve element 72 isaxially longer than in the embodiment shown in FIGS. 2 and 3 andincludes, near its upper edge, one or a plurality of radial holes 84. Inthe closed position of valve element 72 shown in FIG. 4, radial holes 84are covered by the wall of bore hole 66, and the entirety ofthrough-channel 78 of connector element 72 is available forthrough-flow, whereas in the closed position shown in FIG. 5, hole orholes 84 are open to connector bore hole 64 and through-channel 78 isclosed off in the upward direction because end faces 70 and 80 areresting against one another.

Hydraulic actuation systems of the type described are produced in largevolumes and it is important that there be an inexpensive andfunctionally reliable connection between hydraulic medium line 14 andcylinder units 10 and 12.

FIGS. 6 and 7 show an axial section through and a perspective view of aconnector of this kind.

Cylinder 22, i.e., its housing, ends in a cylindrical attachment part86, in which an insertion channel 88 for the insertion of hydraulicmedium line 14 (FIG. 1) which ends as pipe 90, is provided. Theinsertion channel, which is connected to working chamber 62 of cylinder22, enlarges its diameter at a first step 92 and then again at a secondstep 94 which is axially at a distance therefrom, and then ends after athird step 96 at which the diameter is reduced. The section betweenfirst step 92 and second step 94 has an inner diameter which roughlymatches the outer diameter of pipe 90. As shown in FIGS. 6 and 7,locking element 98, which is as a whole cylindrical, is inserted fromthe left into insertion channel 88, has an inner diameter which matchesthe outer diameter of the pipe, protrudes with front end-section 100into an annular space between second step 94 and third step 96, andextends back against third step 96. Locking element 98, which is madeof, for example, plastic, has on its outside fingers 102, which arepositioned at a distance from one another around the circumference, forexample offset by 180° from one another, may be pushed onto the slightlyconical outer surface of attachment part 86 subject to elasticexpansion, and extend back against annular rib 104 of attachment part 86in a form-locking manner. Before locking element 98 is pushed ontoattachment part 86, at least one sealing ring 106 is placed in theannular space between steps 94 and 96.

The inward movement of locking element 98 relative to attachment part 86(to the right as shown in the figures) is limited because the front endof attachment part 86 rests against locking element 98 within fingers102, which ensures that sealing ring 106 is not forcibly misshapen whenlocking element 98 is inserted.

At its left-hand end-section 109, as shown in the figures, the lockingelement has an annular space 108 formed by the stepped design, which atthe right-hand side as shown in the figures forms a stop surface 110 fora projection 112 on pipe 90. At its left-hand end, annular space 108surrounds projection 112 in a form-locking manner. From the left, alocking sleeve 114 is placed onto locking element 98 and has fingers 116which, when locking sleeve 114 is in the appropriate rotated position,overlap fingers 102 of locking element 98 and hold them against theouter surface of attachment part 86. Locking sleeve 114 functions as abayonet in conjunction with locking element 98 via correspondingdiagonal surfaces.

The described system is assembled as follows:

Sealing element 84 is inserted into insertion channel 88. Next, lockingelement 98 is inserted, and locking sleeve 114 is pushed onto lockingelement 98, its being feasible to push it on in a rotated position,locking between locking sleeve 114 and locking element 98 then occurringafter locking sleeve 114 has been rotated by 90°. Thus the assembly ofsealing element 106, locking element 98, and locking sleeve 114 may bepre-mounted on cylinder 22. To create a connection with the hydraulicmedium line, pipe 90 is inserted from the left through locking sleeve114 and locking element 98 into insertion channel 88 until projection108, which forms a single component along with pipe 90, comes to restagainst stop surface 110 after end-section 109 of locking element 98 hasbeen gently elastically expanded. The end face of pipe 90, which isshown on the right in the figures, is then at a distance from step 92,and sealing element 106 creates a reliable seal between pipe 90 andattachment part 86. Next, locking sleeve 114 is rotated so that itpresses end-section 109 of locking element 98 so that there isform-locking contact with projection 112 and so that its fingers 116press fingers 102 so that they rest in a form-locking manner against theouter surfaces of attachment part 86. In this way, pipe 90 is attachedreliably to attachment part 86 so that there is a seal.

Of course the described system may be modified in many ways. Forexample, projection 112 of pipe 90 is not needed if pipe 90 is only tobe held in place by friction. Nevertheless, with the described undercutsa particularly reliable positive lock between the individual components,which hold pipe 90 axially in place on cylinder 22, may be achieved.

FIG. 8 shows a particularly straightforward embodiment of projection 112of pipe 90. As shown in FIG. 8, projection 112 may be created in astraightforward manner by compressing pipe 90 axially so that a radialbulge is created. This means inexpensive pipe produced by the meter maybe used for the hydraulic medium line, i.e., pipe 90.

The patent claims filed with the application are formulation proposalswithout prejudice of the achievement of broader patent protection. Theapplicant reserves the right to claim additional feature combinationspreviously only disclosed in the description and/or the drawing. Theback-references used in the subclaims indicate further refinements ofthe object of the main claim by the features of the particular subclaim.They are not to be understood as a waiver of obtaining independentobjective protection for the combinations of features of theback-referenced subclaims. Because the objects of the subclaims may formseparate independent inventions with respect to the related art on thepriority date, the applicant reserves the right to make them the objectof independent claims or division clarifications. They may furthermorealso contain independent inventions having a design that is independentof the objects of the aforementioned subclaims.

The exemplary embodiments are not to be understood as limitations of thepresent invention. Rather, numerous modifications and variants arepossible within the present disclosure, in particular variants,elements, and combinations and/or materials that are obvious to thoseskilled in the art regarding the achievement of the object or theachievement of advantages, for example, by combination or modificationof individual features or elements or method steps described inconjunction with those in the general description and embodiments aswell as in the claims and contained in the drawing, resulting in a newobject or new method steps or method step sequences via combinablefeatures, including those concerning manufacturing, testing, and workmethods.

1-16. (canceled) 17: A hydraulic actuation system, comprising: a mastercylinder unit; a slave cylinder unit; a hydraulic medium line connectingthe master cylinder unit and the slave cylinder unit; and a throttlevalve for adjusting a flow resistance between cylinders of the mastercylinder unit and the slave cylinder unit. 18: The actuation system asrecited in claim 17, further comprising: an actuator configured toactuate the throttle valve; a piston sensor configured to detect amovement of a piston in at least one of the cylinder units; and acontrol unit connected to the piston sensor and controlling theactuator. 19: The actuation system as recited in claim 18, wherein theactuation system is configured to actuate a vehicle clutch, wherein thepiston sensor detects movement speed of the piston of the mastercylinder unit, and, if the speed exceeds a predefined value as theclutch engages, the control unit triggers the actuator to reduce athrough-flow cross section of the hydraulic medium line. 20: Theactuation system as recited in claim 19 further comprising an engineactuator configured to increase an output of an internal combustionengine of the vehicle if the piston reaches a predefined position and/orthe piston speed exceeds a predefined value as the clutch engages. 21:The actuation system as recited in claim 19, wherein the control unit isconnected to at least one of a wheel sensor configured to detect arotational speed of a vehicle wheel and a transmission ratio sensor. 22:The actuation system as recited in claim 1, wherein the throttle valveincludes a connector bore hole leading to a working chamber of one ofthe cylinder units, a bore hole extending at a substantially right angleto the connector bore hole, and a valve element disposed in the borehole and moveable by a flow of the hydraulic medium between the cylinderunits to a stop position in contact with the stop, in which a flow crosssection of the throttle valve is reduced. 23: The actuation system asrecited in claim 22, wherein the valve element is pipe-shaped andincludes an axial through-channel having a channel wall and a radialopening in the channel wall, the valve element being moveable from afirst position, in which hydraulic medium flowing out of the workingchamber flows through the through-channel, to the stop position by thehydraulic medium flowing into the working chamber, in which an end faceof the valve element rests against the stop at least partially closingthe through-channel, and the hydraulic medium flows through the radialopening. 24: The actuation system as recited in claim 22, wherein thebore hole is disposed in a housing of the respective cylinder unit andthe pressure medium line is connected to the bore hole. 25: Theactuation system as recited in claim 22, wherein the throttle valve isassigned to the master cylinder unit of a vehicle hydraulic clutchactuation system and reduces the flow cross section of the flow ofhydraulic medium into the master cylinder. 26: A device for connecting apipe-shaped hydraulic medium line to a connector on a housing, thedevice including: a cylindrical attachment part of the housing includingan insertion channel; a pipe disposed within the insertion channel anddefining an annular space between an outside of the pipe and an insideof the insertion channel; a radial annular surface delimiting an axiallyinward end of the annular space; a cylindrical locking element having afront end section and a rear end section and insertable into theinsertion channel, wherein in an inserted state, the front end-sectionprotrudes into the annular space and the rear end-section lies outsidethe cylindrical attachment part; at least one sealing ring disposable inthe annular space between an end face of the locking element and theradial annular surface; and a locking sleeve rotatable relative to thelocking element and from an unlock position, in which the pipe isinsertable through the locking sleeve and locking element beyond theannular surface of the attachment part and into the insertion channel,to a lock position, in which the pipe is held axially against theattachment part by one of the locking element and the locking sleeve.27: The device as recited in claim 26, wherein the housing houses one ofa master cylinder and a slave cylinder. 28: The device as recited inclaim 26, wherein, in the inserted state of the pipe, the front endsection extends back through the annular space. 29: The device asrecited in claim 26, wherein an outward end of the annular space isdelimited by a radial holding surface, the front end section including acounter surface resting against the holding surface. 30: The device asrecited in claim 26, wherein a rear end section of the locking elementhas a radially inward stop surface and wherein the pipe has a projectionresting against the stop surface. 31: The device as recited in claim 30,wherein the stop surface delimits the annular space, which overlaps theprojection. 32: The device as recited in claim 30, wherein theprojection includes an annular bulge. 33: The device as recited in claim26, wherein the locking element has at least two locking element fingersdisposed diametrically opposite one another and resting against anoutside of the cylindrical attachment part, wherein the locking sleevehas at least two locking sleeve fingers, and wherein, in the lockposition, the locking element fingers and the locking sleeve fingers arepressed into engagement with the outside of the cylindrical attachmentpart in a form-locking manner.